This invention relates to motorized tools for extruding semi-dense materials such as sealants and similar materials.
In particular, the invention concerns such a motorized tool comprising a body in pistol form containing a screw and nut system driven by means of an electric motor to move a piston borne at one end of the screw, in which said motor is of the reversible type and is controlled by means of a trigger switch which can be pulled back to actuate the motor and in front of which is a switch for selecting the rotation direction of the motor.
Tools of this type are known: for example, German patent DE-C-3842767, European patent application EP-A0463990, U.S. Pat. No. 5,027,984 and, in particular, Italian application for registered utility model no. TO93U000049 in the name of Stefor Srl, assigned to the Applicant. In the motorized tool described in that document, which envisages a friction clutch device for releasing the screw of the actuating unit to rotate freely if the resistance to the movement of the piston is of a greater magnitude than a predetermined value, the selector switch governing the direction of rotation of the motor consists of a lever pointed towards either side of the tool to switch the rotation direction of the motor so as to correspond either to the forward or to the reverse movements of the screw with the piston.
This solution, while being relatively simple and effective, can lead to jamming and therefore to delays, particularly as far as the reverse movement of the piston at the end of the extrusion operation is concerned, with the consequence that it causes further undesired quantities of sealant or similar substance to come out of the tool.
A further problem with known motorized tools resides in the difficulty in setting the speed of flow of the sealant or similar substance from the tool with precision and its adjustment is entrusted to the sensitivity of the operator.